The present disclosure relates to a backlight unit capable of improving light efficiency and assemblability and a liquid crystal display device having the same.
Based on rapidly developing semiconductor technologies, demands on compact and light flat display devices with high performance are drastically increased recently.
A liquid crystal display device (LCD) receiving public attention recently among the flat display devices has various advantages such as compactness, lightness, and low power consumption. That is, the LCD gradually attracts public interest as a substitute means capable of overcoming limitations of a cathode ray tube (CRT) and thus becomes widely used in almost all information processing devices that require a display unit.
The LCD injects a liquid crystal material between a color filter substrate having a common electrode and a color filter and an array substrate having a thin film transistor and a pixel electrode, and then applies respectively different electric potentials on the pixels electrode and the common electrode. Therefore, the LCD changes arrangements of liquid crystal molecules, thereby adjusting transmittance of light in order to display an image.
Since a liquid crystal display panel including the color filter substrate, the array substrate, and the liquid crystal is a light receiving device that does not emit light by itself, it includes a backlight unit at its bottom in order to provide light.
The backlight unit includes a light source, a light source housing surrounding the light source to prevent light loss, a light guide plate converting a light emitted from the light source into a plane light, a reflective sheet disposed on the rear of the light guide plate, and optical sheets disposed on the light guide plate.
The light source extensively uses a cold cathode fluorescent lamp (CCFL) having relatively less emitted heat and a long life span and also generating a white light close to a natural light. Additionally, a medium/small LCD commonly uses a light emitting diode (LED) having compactness, excellent color reproduction, and also less power consumption.
FIG. 1 is a perspective view of a related art liquid crystal display device. FIG. 2 is a cross-sectional view taken along a line I-I′ of FIG. 1.
As illustrated in FIGS. 1 and 2, the related art liquid crystal display device includes a liquid crystal display panel 11 for displaying an image, a backlight unit disposed at the bottom of the liquid crystal display panel 11 to provide light, and a top case 10 surrounding the edge of the liquid crystal display panel 11 and coupled to the backlight unit.
The backlight unit includes a support main 20 having a rectangular frame, a bottom cover 70 disposed on one side of the support main 20, a light emitting diode 50 disposed on one inner side of the bottom cover 70, and a light guide plate 40 disposed on the same plane as the light emitting diode 50.
Additionally, the light emitting diode 50 is mounted on the flexible printed circuit board (FPC) 51, and optical sheets 30 are disposed on the light guide plate 40.
First and second reflective sheets 61 and 63 are disposed at a region having the light emitting diode 50 to guide light toward the light guide plate 40. Therefore, light loss can be reduced.
However, because the related art liquid crystal display device has a structure where the second reflective sheet 63 is disposed on the FPC 51 and the light guide plate 40 is disposed on the reflective sheet 63, it is difficult to assemble an outgoing side 53 of the light emitting diode 50 and an incident surface 43 of the light guide plate 40 to respectively correspond to each other. That is, if the outgoing side 53 of the light emitting diode 50 and the incident surface 43 of the light guide plate 40 are not disposed to correspond to each other, there may be a region where no light reaches and thus light efficiency can be deteriorated.
Furthermore, because a uniform interval between the incident side 43 and the FPC 51 is maintained due to the FPC 51 and the second reflective sheet 63 in the related art liquid crystal display device, its assemblability can be deteriorated if the light guide plate 40 moves freely or defective alignments occur.